Chronic total occlusions (CTO) are vascular lesions that are totally occluded. These can occur anywhere in the human body such as coronary, carotid, visceral, iliac, femoral, and popliteal arteries and veins. Usually these lesions will develop over the course several months to years. Due to chronicity of their natural course, there usually will be an adequate amount time to for development of collateral vessels to supply blood to tissue. However these collateral vessels barely provide enough blood flow to keep the end organs alive and are inadequate to support the function of dependent organs.
Chronic total occlusions can have serious medical consequences depending on their location. For example, blockages located in coronary arteries can cause heart muscle damage and heart failure, whereas blockages located in femoral and popliteal arteries can cause leg ulcers and gangrene.
Chronic total occlusions per se are not “total occlusions”, but rather contain several intrinsic nonfunctional narrow channels. Traditionally, hydrophilic coated guidewires are used to penetrate through one or more of these narrow channels to create a contiguous passage between open vessel segments proximal and distal to occlusion. This passage is subsequently dilated to accommodate therapeutic devices such as balloons or stents.
Various surgical and minimally invasive methods have been in vogue for many years for revascularization of CTOs. Surgical grafts, have been for many decades, designed to bypass blockages in coronary or peripheral vessels. Minimally invasive technologies include guidewires or CTO devices.
CTO lesions frequently contain extremely hard and calcified plaques, which makes them impenetrable. Guidewires, when used in CTOs, are sometimes risky as they can inadvertently damage or more ominously perforate the vessel wall. Often, the guidewire tip has insufficient support, and can buckle during an attempted penetration into the calcified plaque. The guidewire, when forced into a CTO, can also inadvertently be misdirected by the operator in an unintended direction, creating a dead end plane between the vessel wall and the plaque (i.e. a subintimal plane). If the guidewire fails to create successful passage through the CTO, the resulting subintimal tract prohibits the use of subsequent therapeutic devices such as a balloon, stent or atherectomy catheter. Another drawback in CTO devices includes shafts that are not robust enough to resist kinks when advanced inside of a CTO. Still another drawback is that the CTO device is not easily controlled, whereby the tip of the CTO device veers eccentrically away from the center of the blood vessel when the CTO device is pushed though the CTO. Due to these drawbacks, success rates with guidewires in CTO revascularization are marginal at best.
Several CTO technologies have been introduced in an attempt to overcome some of the difficulties faced when using guidewires and CTO devices to improve successful CTO penetration rates. In U.S. Pat. No. 6,599,304 Selmon et al, teach “an intravascular catheter system for the treatment of occluded blood vessels that includes tissue displacement or hinged expansion members that are movable from a closed to an open position . . . . A spreading or mechanical force may be thus applied to the vessel wall and occlusion so as to tear, fracture or otherwise disrupt the occlusion adjoining the vessel wall. This disruption of the occlusion may create a channel or passageway of sufficient size for the passage of guidewire or therapeutic catheter around or through at least a portion of the obstruction as part of an overall effort to restore regular circulatory function surrounding the occluded vascular region.”
In U.S. Pat. No. 8,062,316, Patel et al. teach a CTO catheter with a novel rotating cutting head with helical blades at its distal end, the tip is lodged in a protective sheath. “Application of torque to an inner catheter or wire attached to the cutting head applies spin to the cutting head . . . . Depending on the angle and nature of the cutting head's protruding blades, the blades may either may be designed to simply cut through the occluding material, without actually dislodging the occluding material from the body lumen, or alternatively the blades may be designed to both cut through the occluding material, and severe its links to the body lumen, thereby dislodging the occluding material from the body lumen.”
In U.S. patent application Ser. No. 11/090,435, Hong teaches a system for opening CTOs, by using a catheter having multiple channels. In addition, the catheter may have a bullet-shaped distal tip and/or torqueing grooves in the proximal and distal shaft, which will facilitate advancing catheter through CTO with manual torqueing action at the proximal end. Multiple channels running along the length of catheter are distensible and used to advance guidewires, balloons or stents into the lesion.
In U.S. Pat. No. 8,021,330, McAndrew teaches a novel balloon catheter with a “no-fold balloon at a distal end thereof that surrounds a distal portion of a guidewire shaft having a compliant shaft or tubular section for selectively gripping a guidewire there within.” Upon inflation, the compliant soft section of the guidewire shaft locks onto the guidewire. “This provides the clinician a conjoined balloon catheter and guidewire ensemble that together may be pushed through a tight stenosis such as chronic total occlusion.”
In U.S. patent application Ser. No. 12/108,921, Duffy et al. teach a visualization and treatment system for treating CTO. The system includes an elongated member configured to be tracked to the chronic total occlusion. The elongated member has a transducer located at its distal end. Acoustically activated material will be packed at the distal end of elongated member. The system also includes an external imaging system constructed and arranged to create an image of the chronic total occlusion. The external imaging system may also be configured to generate ultrasonic energy waves which in turn vibrate the acoustically activated material located at the distal end of the elongated member. These vibrations in turn produce mechanical energy that may be used to penetrate and cross CTO.
In U.S. patent Ser. No. 13/553,659, Richter teaches an apparatus and method for guided penetration of chronic total occlusion. This invention relates to an apparatus that facilitates accurate placement of guidewire and drilling tip within the blood vessel during recanalization of CTO. It comprises of an imaging system which can detect the lesion, vessel wall and guidewire tip in real-time. “Preferably, this apparatus also facilitates the penetration of a CTO or other obstruction in a vessel. The method of using the apparatus of the invention facilitates treatment of the occlusion and avoids or reduces complications and risks associated with treating the occlusion, such as perforation of walls of the vessel and creation of a false lumen.”
In U.S. Pat. No. 7,763,012 Petrick et al. teach a catheter and method to cross CTOs. The catheter comprises of an elongated tubular member having a deflectable tip at the distal end. “The catheter is advanced to a region of interest in an artery proximal to a lesion. A control wire is operated to direct the deflectable tip toward the lesion. A guidewire is advanced through the lumen of the catheter and into the lesion to cross the lesion.”
In U.S. Pat. No. 8,241,315 Jensen et al. teach an apparatus and method configured to penetrate occlusion while limiting inadvertent vessel damage. This device includes an elongated sheath and a stylet disposed within the elongated sheath. The stylet includes a lumen from proximal to distal ends which will allow passage of a guidewire after the occlusion is penetrated. In use, “the stylet can be moved distally such that the distal region of the stylet penetrates at least partially into the occlusion . . . . After the stylet has extended through the proximal cap, a guidewire can cross through the occlusion . . . . Then the recanalization assembly can be further advanced through the occlusion and the balloon placed near the distal cap and the stylet centered and passed across the distal cap.”
Still, success rates with these new technologies are reportedly varied from 50-70% due to various factors including operator's experience. In addition, costs, cumbersomeness, need for complex preparation and lengthy training required for proper usage of these CTO devices can prohibit their widespread and cost efficient usage. Hence, despite these technological developments, there is still a great need for a simple, safe, easy-to-operate, efficient and cost effective CTO devices.